The present invention relates to a controlling apparatus and a method of an internal combustion engine.
To improve fuel economy and to increase engine power at the same time, engines that change combustion mode between stratified lean combustion and homogeneous stoichiometric combustion according to current running conditions have been introduced. Such engines perform exhaust gas recirculation (EGR). Specifically, the engine recirculates exhaust to an intake system during stratified lean combustion to reduce the exhausted amount of nitrogen oxide and to improve fuel economy. Japanese Unexamined Patent Publication 9-32651 discloses an engine that performs EGR during homogeneous stoichiometric combustion in accordance with the running state to reduce the exhaust of NOx and to improve the fuel economy.
If the running conditions such as the throttle opening and the engine speed are the same, EGR during homogenous stoichiometric combustion reduces the amount of new air drawn into the engine. Specifically, the difference of the new air represents the amount of recirculated exhaust, or the EGR amount. The reduced amount of new air lowers the torque of the engine. Thus, in some engines, when homogeneous stoichiometric combustion is performed with EGR, the throttle opening is widened compared to when homogeneous stoichiometric combustion is performed without EGR. Accordingly, the torque loss due to EGR is compensated for.
In an engine that switches combustion modes, the torque is adjusted by controlling fuel injection amount during stratified lean combustion mode. Also, the torque is adjusted by controlling the throttle opening, or by controlling the amount of intake air, during homogeneous stoichiometric combustion. That is, the control values used for adjusting the torque vary depending on combustion modes. Thus, if the torque of the engine is not properly controlled, the torque is abruptly changed when the combustion mode is switched, which degrades the drivability.
Accordingly, it is an objective of the present invention to provide a controlling apparatus and a method of an internal combustion engine that prevents the torque from abruptly changing when the combustion mode is switched under constant running conditions.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a controlling apparatus of an engine that generates torque by combusting air fuel mixture in a combustion chamber is provided. The engine operates in a combustion mode selected from a homogeneous stoichiometric combustion mode and a stratified lean combustion mode. The homogeneous stoichiometric combustion mode includes a first homogeneous mode and a second homogeneous mode. When the engine operates in one of the first and second homogeneous modes, EGR control, in which some of exhaust gas is recirculated to the combustion chamber, is performed. When the engine operates in the other of the first and second homogeneous modes, EGR control is not performed. The apparatus includes computing means, intake air control means and fuel control means. The computing means computes a torque reflecting value based on the running state of the engine. The torque reflecting value reflects an engine torque demanded when the engine operates in the first homogeneous mode. When the engine operates in the homogeneous stoichiometric combustion mode, the intake air control means controls the amount of intake air drawn into the combustion chamber thereby adjusting the engine torque. When the engine operates in the first homogeneous mode, the intake air control means controls the intake air amount based on the torque reflecting value. When the engine operates in the second homogeneous mode, the intake air control means modifies the torque reflecting value for compensating for the difference of the engine torque between the first and second homogeneous modes due to whether EGR control is performed. The intake air control means controls the intake air amount based on the modified torque reflecting value. When the engine operates in the stratified lean combustion mode, the fuel control means controls the amount of fuel supplied to the combustion chamber based on the torque reflecting value thereby adjusting the engine torque.
The present invention may also be embodied as a method for controlling an engine that generates torque by combusting air fuel mixture in a combustion chamber. The engine operates in a combustion mode selected from a homogeneous stoichiometric combustion mode and a stratified lean combustion mode. The homogeneous stoichiometric combustion mode includes a first homogeneous mode and a second homogeneous mode. When the engine operates in one of the first and second homogeneous modes, EGR control, in which some of exhaust gas is recirculated to the combustion chamber, is performed. When the engine operates in the other of the first and second homogeneous modes, EGR control is not performed. The method includes computing a torque reflecting value based on the running state of the engine, the torque reflecting value reflecting an engine torque demanded when the engine operates in the first homogeneous mode, controlling the amount of intake air drawn into the combustion chamber based on the torque reflecting value thereby adjusting the engine torque when the engine operates in the homogeneous stoichiometric combustion mode, modifying the torque reflecting value when the engine operates in the second homogeneous mode thereby compensating for the difference of the engine torque between the first and second homogeneous modes due to whether EGR control is performed, wherein, when the engine operates in the second homogeneous mode, the intake air amount is controlled based on the modified torque reflecting value, and controlling the amount of fuel supplied to the combustion chamber based on the torque reflecting value when the engine operates in the stratified lean combustion mode thereby adjusting the engine torque.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.